Potential development and utilization of sweet potato flour as a raw material for the food industry

Sweet potato (Ipomoea batatas) is one type of tuber that has an important role in food diversification programs. Each 100g of sweet potato contains 27.9 g of carbohydrates, 7000 SI of vitamin A, 30 mg of vitamin C, 30 mg of mineral Ca and an energy value of 123 calories. Its carbohydrate content ranges from 64.83 to 66.90% which is a potential energy source to meet basic food needs other than rice. Sweet potato is considered as a raw material for the food industry, because it has good nutritional content, short plant life, and high production. Its vitamin B6 and folic acid is needed to optimize brain work, rich in fiber and complex carbohydrates but low in calories which is very good for diabetics. However, the soft texture of sweet potatoes and the high of its water content make sweet potatoes easy to damage due to mechanical influences. Processing into flour is one of the efforts to preserve sweet potatoes and increase their usefulness. Ingredients composition, drying method, use of chemicals, and steaming process are factors that can affect flour quality, especially its color and functional characteristics. Drying methods that can be used are spray drying, drum drying and oven dryer. The aim of this review is to explore the opportunities and potential of sweet potato flour (SPF) as an industrial raw material for processed food industries in Indonesia. The review method used is the reference collection method, which is taken from several research results related to SPF and its application to food products such as beverages, fructose syrup, noodles, flakes, cookies, ice cream, yogurt, jams, dyes, and others. Through the preservation of sweet potato into flour and its use as industrial raw material, it is hoped that it can increase the diversity of functional foods needed by the Indonesian community.


Introduction
Sweet potato is the main carbohydrate source commodity, after rice, corn and cassava.In addition, sweet potatoes have an important role in the supply of food, industrial raw materials and animal feed.Usually, sweet potatoes are consumed as an additional or side dish among Indonesian, except for the areas of Irian Jaya and Maluku.In these two areas, sweet potato is used as a staple food.Sweet potato plants can grow in the lowlands and highlands [1].Indonesia is the second largest sweet potato producer in the world after China [2], sweet potato productivity in Indonesia reaches 180.21 kW ha -1 , production of 1,914,244 tons from a harvested area of 106,266 ha.
The use of sweet potatoes in Indonesia is still limited for conventional processed foods such as boiled sweet potatoes, fried sweet potatoes, sweet potato chips, sweet potato compote, 'getuk' and 'timus'.Little is used for raw materials of food industry.Meanwhile, in developed countries, its utilization has expanded into processed products with high nutritional value and economically profitable.One of the developed countries with the largest consumption of sweet potato is Japan [3].The establishment of an 1230 (2023) 012006 IOP Publishing doi:10.1088/1755-1315/1230/1/012006 2 industry made from sweet potato will have a good chance for the business in Indonesia.In addition to supporting and succeeding in the food diversification program, it is also profitable, as well as creating new jobs for the surrounding community.One of the efforts to promote the superiority of sweet potato as a food ingredient is to introduce the potential of functional food contained in sweet potato.Functional food elements in sweet potatoes include a variety of antioxidants (beta carotene/vitamin A precursor with high concentration), mineral elements, especially iron, dietary fiber, oligosaccharides, and others [4,5].
Based on the color, sweet potatoes are divided into 3 types, namely white sweet potatoes, yellow/orange sweet potatoes and purple sweet potatoes (PSP).Among the three types, PSP has the highest anthocyanin content.This is what causes the purple-black color.PSP anthocyanin content ranges from 33.90 mg/100 g to 560 mg/100 g and acts as an antioxidant [6].The anthocyanin content in PSP not only has the potential as a natural dye, but can also provide various nutraceutical properties such as free radical activity [7].Sweet potatoes also contain high calcium and their carbohydrate content is classified as having a Low Index (LGI, 54) which means it is very suit able for diabetics.Sweet potato starch includes resistant starch which helps the human body to remove cholesterol and prevent cancer [8].
Sweet potato flour-based food diversification program has good nutritional content, relatively short planting age, and high production.The soft texture of sweet potatoes with high water content is easily damaged by mechanical influences.Processing sweet potatoes into flour is one of the efforts to preserve sweet potatoes and to increase the use of sweet potatoes in the food industry.The use of SPF in food products can add color and sweetness, function as a source of nutrients [9].Moreover, it can be used as a substitute for wheat.
The use of wheat raw materials in the food industry has reached 6.7 million tons in 2020 and is currently rising to 6.9 million tons.Meanwhile, based on data from the Central Statistics Agency [2], throughout 2021 Indonesia's wheat flour imports reached 31.34 thousand tons with a total value of US $ 11.81 million.Indonesia's wheat supply mainly comes from Australia and Ukraine.In 2022, wheat consumption predicted to increase by 5% according to national economic growth.On the other hand, the demand for healthy foods, especially gluten-free foods, is increasing, as some people are gluten intolerant.A gluten-free diet is a must for colic patients and has recently become an option for a healthy lifestyle.Gluten-free ingredients are also an alternative to fight the food industry's dependence on imported wheat.Therefore, there is a huge opportunity to explore the use of local food, especially sweet potatoes as a substitute for flour in the food industry.Processing of SPF makes it more durable and can be enriched with fortification so that its utilization becomes wider.
SPF has the potential to be a local raw material because it: 1) Suit able for the agro-climate of most parts of Indonesia, 2) high productivity, making it profitable to cultivate, 3) nutrients that have an effect on positive on health (prebiotics, dietary fiber and antioxidants), and 4) has the potential to support food diversification programs [10].
The purpose of this paper is to explore the opportunities and potential of SPF as an industrial raw material.One of the opportunities for its use in Indonesia is as a raw material for processed food such as bakery, noodle, dye, and beverage industries.

The nutrient and functional value
The advantage of the functional value of sweet potato is its health benefits.Sweet potato contains high carbohydrates, minerals and vitamins.The comparison of material content in 100g of sweet potato, rice, cassava and corn be seen in table 1.The content of mineral Ca, vitamins A and C are higher than rice, while the calorific value is lower.So it suit able for diet purpose.Sweet potatoes are also useful for treating coronary heart attacks, reducing up to 40% of the risk of hypertension sufferers from having a stroke, their oligosaccharides can prevent constipation and ease bowel movements, prevent Alzheimer's disease or brain aging and COPD (Chronic Obstructive Pulmonary Disease) [11].[12] The compounds comparison among sweet potato can be seen in table 2. PSP has the highest fat, water content, and Anthocyanins, but the lowest in carbohydrate, protein, ash, and vitamin C. The color of sweet potatoes that vary from white, red to purple shows the different pigment content in each type.Anthocyanins are classified as flavonoid pigments which are generally soluble in water.The appearance of the color is influenced by the concentration of pigment and pH.At dilute concentrations or low pH, anthocyanins are blue, and at high concentrations or high pH are purple [13].[14] Carotenoids are a group of yellow, orange and red-orange pigments that are dissolved in lipids (oils).One cup of mashed steamed sweet potato stores 50,000 SI of beta-carotene, equivalent to the betacarotene content of 23 cups of broccoli.By consuming one serving of steamed/boiled red sweet potato, you have met the adequacy of vitamin A 2100-3600 mg per day [11].
Anthocyanins have a primary function as an antioxidant.While beta-carotene functioning as an antioxidant and a source of vitamin A. Molecule of antioxidants compounds can donate free electrons to free radical molecules and break their chain reaction.In addition, antioxidants can prevent the formation of new free radicals by reducing the negative effects of existing free radicals.Antioxidants are divided into 3, namely antioxidants produced by the body in the form of enzymes, natural antioxidants derived from plants or animals and synthetic antioxidants made from chemicals [15].Antioxidants derived from anthocyanins and carotenoids are natural antioxidants.

Physico-chemical characteristics
Factors that affect the quality of processed products are physico-chemical properties (water absorption index, water solubility and viscosity) of raw materials.It is very important to extract this information from SPF/starch, because the use of sweet potatoes in various processed foods is generally in the form of flour.Several studies have been conducted to analyze the physico-chemical characteristics of SPF/starch (table 3).The water absorption index and the solubility value of PSP flour were close to that of wheat flour, which were 1.92 and 6.0%, respectively.[18] Based on its swellability, solubility and slow-digesting starch fraction, starch of PSP can be used as raw material for processed foods.By using high heating temperatures, PSP starch can be formulated into noodles, vermicelli and flakes (table 4 and table 5) [19].The ratio of amylose and amylopectin will affect the degree of swelling and texture of snacks, also the solubility and degree of starch gelatinization.The greater the amylopectin content, the starch will be wet, sticky and tend to be less [17,18].[20] The chemical composition and bioactive components of PSP flour ranged from 1.08-3.09%protein, 0.17-0.41%lipid, 2.49-2.78%ash, and 94-95% carbohydrates [21].The expanding ability and solubility of sweet potato was low, they are range at 3.40-3.68(g/g) and 8.61-9.56,respectively.However, by going through a process of physical or chemical modification, their starch can still be used as a raw material for cakes [22].

Utilization of sweet potatoes in the food industry
Flour from sweet potato has a size of 80 to 100 mesh.There are 3 quality criteria that must be met by a flour product according to the Indonesian National Standard, namely chemical, physical, and microbiological quality.The physical qualities that must be met include the maximum composition of water, ash, and fat content, which are 10%, 3%, 1%, respectively, and the minimum levels of protein, crude fiber and carbohydrates are 3%, 2% and 85%, respectively.Physical qualities that must be met include normal color, not containing foreign objects, and a minimum level of smoothness of 95%.Meanwhile, from microbiological quality, flour must meet the maximum limit of microbial contamination set by BPOM [23].
Physico-chemical properties of SPF are strongly influenced by temperature and drying time, size of sweet potato slices during drying, and drying method.The quality of SPF that is dried at high temperatures and for a long time has high expansion and solubility properties, making it suit able for baking products.The size of the sweet potato slices affects the gelling properties of flour [24].The drying method by steaming in a drying drum resulted in a higher total phenolic content and antioxidant activity of SPF compared to that produced by a hot air oven dryer [25].
The use of SPF in food products can add natural sweetness, color, taste, and nutrients [26].However, there is an element that needs to be considered in the process of making PSP flour, it is the high content of anthocyanin pigments.Although safe for consumption, non-toxic, and does not cause genetic mutations, anthocyanins can be easily degraded by several factors including pH, temperature, structure, light, oxygen, solvents, enzymes and metal ions [27].Therefore, the processing must include product protection and safety, as well as color quality control.
Steaming and boiling sweet potatoes before drying with drum drying, can maintain the purple color of PSP flour.In addition, it also maintains the functional properties of the flour, such as water absorption and health support compounds contained in it (anthocyanin compounds and resistant starch).Steaming showed a better effect than boiling in terms of flour quantity (243.02g/100 g vs 180.87 g/100 g), total anthocyanin content (121.71mg/100 g vs 83.72 mg/100 g), and content of resistant starch (3.06 g/100 g vs. 2.53 g/100 g) [28].Soaking PSP using 0.01% citric acid resulted in PSP flour which had a bright color and fine texture, decreased ash content and reduced sour smell [29].[32] Sweet potato carbohydrate content is almost the same as wheat flour but with a higher fiber content.Comparison of the nutritional content of SPF with wheat flour is presented in table 6. SPF can be used to substitute wheat flour for manufacture of pastries and cakes.It also can serve as a thickener in soups, breads, and other artificial snacks.The yield of fresh sweet potato for flour is in the range of 20% -30% of the wet weight.
The main component of SPF is carbohydrates which are served as starch.Like other types of native starch, sweet potato starch has poor physical and chemical properties for further processing, so modifications are needed.Physical modification of sweet potato starch was carried out using the autoclaving-cooling method with a 15-30 minutes steaming and drying method in the oven or under the sun.This kind of starch modification produces SPF with a granular structure that can expand and crack, lower starch content, higher freezing and thawing stability, higher water absorption index, and lower hot and cold viscosities [18].
There is also an autoclaving retrogradation method that produces SPF with the best functional properties.The best starch with this methode obtained from red SPF which contains 44.64% dietary fiber, 19.75% resistant starch, 13.5% starch digestibility and 66.32% antioxidant activity [33].High resistant starch (RS) functions as a prebiotic that is useful for preventing constipation and flatulence in the body.This is possible because RS can bind and maintain the water content of feces [34].

Food industry product
SPF/starch can replace wheat flour for bakery products, extruders, cookies, fillers, natural dyes, beverages and additives for baby porridge.The mixture of sweet potato starch in bread can reach 10-20%.Bread made with the addition of 10% sweet potato and mung bean composite flour produced the best bread properties with a color value of 58.87%; swelling power 108.13 ml; texture 147,767 gr; water content 21.17%; ash content 0.495% and total protein content 4.16% [35,36].
Bread made from starch and flour of orange sweet potato, breadfruit flour, mocaf, and breadfruit starch, has the attributes of color, specific volume, protein content, fat content, crude fiber content and sensory properties acceptable to consumers, if the ratio is 10:50 :10:20:10 [37].Bread made from a mixture of wheat flour and sweet potato with a composition ratio of 90:10, significantly (p < 0.05) could increase the protein content compared to bread made from 100% wheat [38].
Bread made from a mixture of PSP flour 15% +1.0%GMS has an IC50 value of 55,833.78ppm DPPH (an increase of 86.06% from bread made from wheat flour) and contains 29.23% water, 7.18% fat, 4.65% protein, 0.93% ash, 58.01%carbohydrates and 4.30% dietary fiber [39].Chinese steamed buns (CSB) with 50% PSP can increase antioxidant activity, polyphenols/anthocyanins and overall sensory reception, also decrease glycemic response [26].Bread substituted with 5-10% SPF can result in a decrease of farinograph and alveogram.Bread hardness increases with increasing SPF.So, the use of SPF should be limited to 5-10% of the mixture [40].
For dry and wet noodle products, substitution of SPF ranges from 10-85%.Dry noodles with a mix of 85% PSP and 15% gluten have a total energy value of 291.18 kcal: 25.59 kcal from protein, 21.68 kcal from fat, and 243.92 kcal from carbohydrates [41].While the application of SPF in making wet noodles produced noodles with a moisture content of 7.19%, ash 2.44%, carbohydrates 49.77%, protein 1.62%, fat 1.38%, and crude fiber 4.59%, with an acid degree of 9.27 NaOH 0.1 N/100 g and has antioxidant activity capable of inhibiting free radicals up to 48.12% [42].The addition of SPF up to 40% can optimize the elasticity of noodles, total phenol content and antioxidant activity.SPF also has the potential to improve the microstructure and increase the nutritional value of noodles [43].
Utilization of 40% PSP in the Flaky crackers formula, resulted in a product with a fiber content of 10.8 g per 100 g product and energy content per serving (216 kcal), it meet 10% of the energy needs of adolescents aged 16-18 years [44].PSP levels of 40-50% in biscuit products can increase the nutritional value and benefits for health, and have a high potential to be accepted by consumers [45].
SPF can also be used for making instant rice and baby porridge.Making sweet potato instant rice can be done by peeling, cutting, soaking sweet potato in a solution of Na-Hydrogen Carbonate and Na-Phyrophosphate (1%:0.05%).Then steaming, size reduction, and drying using an oven for 3 hours or drying in the sun.Sweet potato instant rice is served by soaking it in cold water for about 5 minutes, then drained and steamed until soft and ready to eat.The form of sweet potato instant rice is granules [32].
The beverage product made from 25% PSP has anthocyanin content of 288.89 mg/100 g, and 8.38% reducing sugar, so that the sweetness is appropriate based on the organoleptic results.The process of making beverages is carried out using an enzymatic hydrolysis process [6].
Sweet potatoes are also a potential source of natural dyes because of their beta carotene and anthocyanin content.Natural dyes from sweet potatoes can be obtained by maceration extraction method using 96% ethanol as solvent [27,47,48].The best yield was 4.87% at a temperature of 500ºC with a pressure of 2 atm and at a maceration time of 30 hours, with the equation y= 0.063x + 2.904 and R2 = 0.972.While the anthocyanin levels obtained were 11.01 mg/mL at a temperature of 300ºC with a pressure of 1 atm and at a maceration time of 30 hours, with the equation Y= 0.189x + 5.489 and R2 = 0.974 [27].
Sweet potato can also be used as an ingredient for the manufacture of glucose syrup through enzymatic hydrolysis since it has anthocyanin pigments and high antioxidant activity.Glucose syrup is generally used as an additional raw material for the beverage and food industry, such as ice cream, marshmallows, and sugar confectionaries [49].

Development prospects and obstacles
Sweet potato is one of the plants with wide adaptability.They can live anywhere, from the highlands (> 1500 m asl), to the lowlands with an altitude of 500 m asl.However, if planted at an altitude of > 700 m asl, the yield tends to decrease.There are many different ways of cultivating sweet potatoes, but the management of soil and water is an aspect that farmers are very concerned about.Sweet potato is mostly cultivated in dry land and only a small part is grown in paddy fields.The soil types also vary: from alfisols and ultisols, to inceptisols which generally have low fertility levels [50].
The Ministry of Agriculture through the Directorate General of Food Crops has developed a sweet potato planting program covering an area of 2,000 hectares (ha) in several locations in Indonesia in 2022.In addition, the Ministry of Agriculture has also issued a Minister for a corporate-based local food development program to produce quality commodities, productivity high, and managed throughout the downstream.Products will be well packed to get added value and guarantee export market.So that farmers are expected to get a management pattern through farmer corporations.The national economy will hopefully increase through local food potential from rural areas, especially from sweet potatoes [51].
As one of the functional foods, sweet potato can enrich the diversity of food in Indonesia and at the same time can serve as a healthy food with high nutritional value.Therefore, the development of processed sweet potato and its derivative products will support the food diversification program.Along with the changing trend of people's consumption patterns towards healthy food products, the sweet potato-based processed food market is still widely open.
Some of the obstacles in the use of sweet potatoes are the low awareness of the community about the potential of sweet potatoes, the limited equipment that supports the development of ready-to-eat processed products, and the limitations of farmers in terms of cultivation (fertilization, pests and diseases control, and post-harvest handling).Therefore, the government must seriously facilitate the processing industry so that it becomes a stimulant for sweet potato product developers.

Conclusion
Sweet potatoes have great potential to be a nutrient-rich food source.Sweet potatoes contain high carbohydrates, anthocyanins and beta carotene, also function as antioxidants and precursors of vitamin A which are beneficial for health.Among various types of sweet potato, purple sweet potato (PSP) has the most potential to become one of the functional foods because it has the highest anthocyanin content.In order to increase its utilization in the food industry, it is necessary to dig deeper into its physicochemical characteristics since they affect the selection of processing methods and the quality of the resulting product.So, in the end, it will meet the product requirements of the food industry and can reduce dependence on wheat flour.In addition, to improve the image of sweet potato-based products, it is necessary to produce special products that not only function as substitutes for wheat flour, but are also useful in pharmaceutical products, cosmetics and other non-food products.To develop the potential of sweet potato as a food and industrial ingredient, it is necessary to disseminate training to farming communities, extension workers and sweet potato entrepreneurs.

Table 1 .
Nutritional and calorie content per 100 g of sweet potato, rice, cassava and corn

Table 2 .
Compounds contained in 100 grams of sweet potato

Table 4 .
Amilograf Properties of Sweet Potato Starch

Table 6 .
Nutritional content of SPF and casava flour